Effect of reaction temperature on surface morphology and photoelectric properties of ZnO grown by hydrothermal method in mixed solvent

ZnO thin films were prepared by hydrothermal method in mixed solvent with different reaction temperatures. Microstructure, surface morphology, optical properties and UV photoresponse of the thin films have been investigated by means of X-ray diffractometer, scanning electron microscopy, laser micro-Raman spectrometer, UV–Vis spectrophotometer and interactive source meter instrument. The results indicated that ZnO thin films consist of ZnO nanoparticles with hexagonal wurzite structure. A small quantity of Zn(OH)₂ appear as reaction temperature increase to 125 °C. ZnO thin film grown at 175 °C consists of many densely vertically aligned ZnO nano rods on the substrate and has the best preferential c-axis orientation. Three peaks centered at about 446, 568 and 1150 cm⁻¹ have been attributed to E ₂(high), A ₁(LO) and 2A ₁(LO) phonon mode. Broadening of the visible emission band may be attributed to abundant surface defects and surface states of the thin films. Variation of the E _g may be attributed to the synergy of surface morphology and oxygen-vacancy (V_O) density. The fast and slow UV photo response may be attributed to the adsorption and photo desorption of oxygen molecules on the surface of ZnO thin films and exchange process between oxygen gas and native deep defect level, respectively.